Real Dictionary

code name
A code name is a name used for someone or something in order to keep their identity secret.

code name in American English
noun: a name assigned to conceal the real identity of a person, as a spy, or to conceal the existence or purpose of a plan, military operation, etc

code name in British English
noun: (esp in military and police use) a word used to identify a classified plan, operation, etc
verb: to assign a code name to (a person, group, or operation)

code-name in American English
transitive verb: to assign a code name to

code-name in British English
to assign a code name to (a person, group, or operation)